(1) Field of the Invention
The present invention relates to an image forming apparatus such as a digital copier, facsimile machine, digital printer, plotter etc., and more particularly relates to an image forming apparatus in which an image is formed on a recording medium by causing the developer to jump thereto.
(2) Description of the Prior Art
There have been known image forming apparatuses which, in accordance with an image signal, form a visual image on a recording medium such as paper etc. Japanese Patent Application Laid-Open Hei 7 No. 25,057, for example, discloses an image forming apparatus wherein a toner image is formed, in accordance with an image signal, on a recording medium by causing the toner as the developer to jump whilst the voltage being applied to a control electrode which is placed in the jumping path of the toner is varied.
More specifically, the control electrode of this apparatus, has a number of gates to be the passage holes for the toner, which are arranged grid-wise, i.e., at regular intervals in the conveyed direction of the recording paper, creating a predetermined resolution, arranged in a 4 gate unit slant-wise in the direction perpendicular to the conveyed direction, forming a coarse pitch. In this arrangement, the potential of the gates is controlled in a regular cycle in a time-divisional manner in accordance with the image signal, so as to control toner transfer, to form a toner image on the recording paper.
However, in accordance with the above conventional apparatus, when the potential of the gates is controlled in a time-divisional manner with respect to the perpendicular direction to the conveyed direction of the paper (to be referred to hereinbelow as the row-direction) in order to attain the predetermined resolution with respect to the conveyed direction of the paper, it is necessary to take into consideration the relationship between the pitch between the gates with respect to the conveyed direction of the paper and the conveying speed of the paper to be recorded, and this has complicated the driver control of the gates.
Besides, if the relationship between the pitch of the gates with respect to the conveyed direction of the recording paper and the conveying speed of the paper is not correct, the control signal becomes inactive, as shown in FIG. 1, from the time when the time-divisional switching control of control electrodes S1-S4 for one line has been completed based on the line synchronizing signal to the time when the next time-divisional switching control starts, thus resulting in reduction of the effective time available for printing.